BodhránBot Brains – Choosing a Microcontroller

As the title of this post suggests in this post we will look at the options available for controlling the Bodhrán Bot. We will need to use a microcontroller in order to control the solenoids and have them hit the drum with rhythm. If you followed the links on the previous two posts you will notice that the most popular microcontroller used in solenoid drumming projects (by a long shot) is the Arduino. In fact the growth in popularity of solenoid drumming during the latter part of the last decade has been largely attributed to the emergence of Arduino (in 2005) and similar easily programmable hobbyist microcontrollers. The standard approach is to program the microcontroller to understand midi messages that can be expressed by the solenoid. The important midi information for a solenoid would be the note number (solenoid identification), note on (hit) and velocity (how hard it hits; loudness). If we use motors in the project we might want some kind of modulation information (constant pressure for dampener element) to be understood also. Midi will be used for a number of obvious reasons. As the standard electron music information protocol it has the ability to transfer all the information required. Also because it is widely used it means that our finished instrument can be programed by a huge range of software and hardware devices. If you are planning on taking the Arduino route you should start here, here and here and getting an Arduino Motor Shield will save you a lot of work. You should also look at Randy Sarafan’s Instructable we mentioned in the previous post.

I mentioned in the previous post how the Bodhrán differs from other drums when it comes to how it is played. The beating of the drum skin is only half of the action needed. Changing the tone and resonance through pressure and contact with the back of the drum skin is the other half. Because of time constraints and other commitments we have selected to use the Midi-Switcher (video above) for the solenoid drum beat aspect (and possibly the tone and resonance control… we’ll see). The Midi-Switcher is an Open Source kit (available on Tinde here) which is specifically designed to translate Midi information into physical actions using solenoids . With a little configuration this little device does exactly what we need so it will save us loads of time. There are clear instructions on how to build and configure it at the link above. The convenience of the Midi-Switcher does come at a price however. You can potentially connect eight solenoids or motors but current is limited to 3maps in total and 1 amp per connection. This limits the power of the solenoids we can use or we risk overloading the circuit. In order to achieve the change of tone we need to use a different strategy for the back of the bodhrán. Solenoids are not ideal for applying continued pressure (although latching solenoids could be used) so we have decided to use Universal Power Door Lock Actuators which are cheap and ideally suited to our purposes. They are based on a DC Motor but unfortunately they require a 2 amp current so my next post will detail how we use transistors to bypass the current limitations of the midi-switcher.